I purchased an sd40 3 days ago out the box..430$. The ammo won't feed,,it jams everytime I cock it.. It seems the gun is defective... What will they do?

Make sure you aren't riding the slide. Take it in and let them check it. Bring ammo you are using.

Right

Let the slide retract on its own. You can't push it to load the cartridge - pull it all the way back and let it slingshot by itself. That should seat the bullet properly and solve your issue. Have someone show you if my description is confusing.